High-voltage generator



Dec. 26, 1967 A. v. CREWE ET AL 3,360,663

HIGH'VOLTAGE GENERATOR Filed May 14, 1965 lectron Beam 29cc; 6 Z eratorfiieutrajz Bea/f7? f/caelerator INVENTORS fllbert Zfi Creme IkihikoZ/o/rosazua ,Date ,1. De Geeter /F--( 4 4m [Zia/.1283

United States Patent O 3,360,663 HIGH-VOLTAGE GENERATOR Albert V. Crewe,Palos Park, Akihiko Yokosawa, Naperville, and Dale J. De Geeter, Lemont,IllL, assignors to the United States of America as represented by theUnited States Atomic Energy Commission Filed May 14, 1965, Ser. No.456,013 7 Claims. (Cl. 310-) This invention relates to high-voltagegenerators and more particularly to means for producing a high voltagebetween first andsecond members using an electron beam.

In the particle accelerator field, beam motion is often controlledbypassing the beam between two deflection electrodes mounted in apartial vacuum and having a high voltage established therebetween.Present systems use a conventional high-voltage source with the outputtherefrom cabled to one of the deflection electrodes. A hollow ceramicbushing is mounted between the deflection electrode and the chamberhousing the deflection electrodes. The ceramic bushing is filled withoil and the cable from the source is passed therethrough and connectedto the deflection electrode.

One problem encountered with the present high-voltage system is thetermination of the cable and the bushing at the deflection electrode. Atthe termination and along the cable, electric fields develop to a valuesuch that the oil and other insulation materials contained within thebushing deteriorate, causing electrical breakdown thereof. After thefirst electrical breakdown of the insulation, the insulating propertiesthereof rapidly deteriorate, so that subsequent electrical breakdownsoccur more easily and the system has to be dismantled, cleaned, thecable repaired, and new oil inserted therein. Further, with anelectrical breakdown discharge in the partial vacuum, the surface of theceramic insulating bushing tends to accumulate a film coating of metal,thereby requiring removal and cleaning thereof. The present systems asdescribed are limited to voltages up to 500 kv., continuous dutyoperation becoming increasingly diflicult as one approaches the 500 kv.value.

Accordingly, it is one object of the present invention to provide meansfor generating a high voltage between two electrodes spatially mountedwith respect to each other in a partial vacuum.

It is another object of the present invention to provide means forgenerating a'voltage in excess of 500 kv. between two electrodesspatially mounted with respect to each other in a partial vacuum. I It is still another object of the present invention to provide means usingan electron beam for generating a voltage in excess of 500 kv. betweentwo electrodes spatially mounted with respect to each other in a partialvacuum.

Otherobjects of the present invention will become more apparent as thedetailed description proceeds.

In general, the present invention comprises a Faraday cupmounted inelectrical connection with one of two electrodes spatially disposed withrespect to each other in a partial vacuum. Means are provided forgenerating and directing an electron beam into the Faraday cup, wherebya negative charge accumulation occurs on the electrode having theFaraday cup attached thereto and a high voltage is developed between thetwo electrodes. Further understanding of the present invention may bestbe obtainedfrom consideration of the accompanying drawings wherein:

FIG. 1 is a representative schematic diagram of an apparatus for thepractice of the present invention; and

FIG. 2 is a representative schematic diagram of the preferred apparatusfor the practice of the present invention.

In FIG. 1 the electrodes 10 and 12 are used to deflect a variable masscharged particle beam passing therebetween. The electrodes are rigidlymounted within an evacuable chamber 14. The electrode 10 is mounted tothe walls of the chamber and electrically grounded therewith. A Faradaycup 16 is mounted in electrical contact with electrode 12 and connectedvia resistor 18 to the wall of the chamber 14. The electrode 12 andFaraday cup 16 are spatially mounted with respect to the walls ofchamber 14 by a standoff insulator 20. The resistor 18 is sealed fromthe atmosphere of the chamber 14 by a ceramic bushing 22 filled with oilor a gas, such as sulfur hexafiuoride. An electron beam accelerator 24,such as a Van de Graafl, is connected via tube 26 to the chamber 14. TheFaraday cup 16 is aligned so that the electron beam from the accelerator24 is captured therein.

In operation, electrons from the electron beam are captured by theFaraday cup 16 to thereby produce a negative charge on electrode 12. Thevoltage between electrodes 10 and 12 follows the formula where Q=thecharge on the electrode 12, and C=the capacitance between the electrodes10 and 12. Electron loss from the cathode 12 will follow three paths,the first, 1;, through the standoif insulator 20, the second, I throughthe resistor 18, and the third, I between the electrodes 10 and 12. Thecurrent I; is very small due to the high resistance of the standoffinsulator 20. The current I varies according to the spacing between theelectrodes 10 and 12. The current I varies according to the value chosenfor the resistor 18. For the purposes of the present invention, theresistor 18 is chosen so that it has a relatively low value, whereby thevalue of the current I therethrough far exceeds I and I and isdeterminative of the potential achieved by'the electrode 12. Thus, thepotential developed on electrode 12 is the product of the current Itimes the resistance of resistor 18. Since I is far greater than I (thecurrent flowing through the insulator 20) and I (the current flowingbetween the electrodes), the current I approaches in value the beamcurrent of the accelerator 24. The potential on electrode 12 is thusvaried in an approximately linear manner by varying the beam current ofthe accelerator '24. In operation, the potential of electrode 12 ismaintained below that of the electron beam whereby the problem of beamdefocusing, as hereinafter described, is avoided. For the embodiment ofFIG. 1, a cylindrical chamber 14, five feet in diameter, and electrodes10 and 12, six feet long x 20 inches wide with a 5-15 cm. gap therebetween, were used. The Faraday cup 16 was 18 inches long with a crosssection of 3.5 x 2.5 inches. Resistor 18 had a value of 5 l0 ohms. Withan accelerator beam current of microamperes at a potential of 800 kv., apotential was established on electrode 12 of 600 kv. The foregoingvalues are merely illustrative for the practice of the present inventionand the present invention is not to be limited thereto. With higher beamcurrents, one may obtain higher potentials on the electrodes with theparameters of the various elements being modified in accordancetherewith.

With the embodiment of FIG. 1, potential regulation of electrode 12 isaccomplished as hereinbefore described by regulation of the beam currentof the accelerator 24. Close regulation of the beam current of anaccelerator is more difiicult than regulation of the potential thereof.FIG. 2 illustrates the preferred embodiment for the practice of thepresent invention, wherein regulation of the potential of electrode 12is accomplished via regulation of the potential of the beam current ofaccelerator 24.

As for the embodiment of FIG. 1, electrodes and 12 are symmetricallydisposed in an evacuable chamber 14. Electrode 10 is mounted to thewalls of the chamber and electrically grounded therewith. A Faraday cup16 is mounted in electrical contact with electrode 12 and connected viaa standofi insulator 20 to the wall of the chamber 14. An electron beamaccelerator 24 is connected via tube 26 to the chamber 14. The Faradaycup 16 is aligned so that the electron beam from the accelerator 24 iscaptured therein.

In the embodiment of FIG. 2, the electrons from the electron beam ofaccelerator 24 are captured by the Faraday cup 16 and deposit theircharge on electrode 12 to raise the potential thereof. The charge on theFaraday cup 16 will increase until it is equal to CV where C: thecapacitance between electrodes 10 and 12 plus the capacitance fromelectrode 12 to the walls of chamber 14 and V=the potential of theelectron beam, at which time only sufficient additional electrons willbe captured thereby to replace electrons lost through the standoffinsulator 20 (I and between the electrodes 10 and 12 (I The upcapturedelectrons in the beam from accelerator 24 are reflected back to thewalls of the chamber 14. Thus, when the potential of electrode 12 equalsthat of the electron beam from accelerator 24, electron capture by theFaraday cup 16 is effected only to replace electrons lost through I and1 As the load or current I between the plates 10 and 12 increases (byvarying the gap therebetween), then less electrons are reflected to thewalls of the chamber 14. The embodiment of FIG. 2. is thereforeself-regulating, since any change betwen the potential of electrode 12and the energy of the electron beam is automatically adjusted by eitherfewer or more electrons being reflected to the walls of the chamber 14.

For operation of the present invention as described supra in theembodiment of FIG. 2, it is necessary that the Faraday cup 16 isdesigned so that any defocusing effect on the electron beam is minimizedas the electrode 12 approaches and equals the energy of the electronbeam. If this is not done, as the potential of electrode 12 equals thatof the electron beam, the electron beam may be deflected so that itnever strikes the Faraday cup 16 or the defocusing effect of theelectric fields about the Faraday cup may become such that inefiicientelectron capture by the Faraday cup results. To minimize any defocusingeffect on the electron beam, it is necessary that the aperture ofFaraday cup 16 have a minimum diameter of approximately two inches. Withthis aperture size, the equipotential lines of the electric fieldsexisting between the cup. 16 and the walls of the chamber 14 penetrateto a depth within the cup 16 sufficient to permit eflicient trapping bythe cup 16. Further improvement in operation may be achieved by insuringthat the length to diameter ratio of the cup 16 has a minimum value ofapproximately 6:1, whereby secondary particle escape from the cup 16will be prevented. For the purposes of the present invention with aFaraday cup having a rectangular cross section, the shortest side of thecross section is used in determining the length to diameter ratio.

With the embodiment of FIG. 2, it is thus seen that the voltage or thepotential of electrode 12 is regulated by the energy of the electronbeam from accelerator 24. To increase or decrease the value of thepotential of electrode 12, it is only requisite that one increase thevalue of the energy of the electron beam from accelerator 24. Since theenergy of an electron beam from an accelerator 24 may be closelyregulated, the potential of electrode 12 is similarly able to be closelyregulated. It is to be noted that the potential of electrode 12 isself-regulating with respect to the electron beam from accelerator 24.Using the same component values as for the embodiment of FIG. 1 (withthe deletion of resistor 18 therefrom), a voltage of 600 kv. wasobtained with a beam current of 300 microarnperes at a potential of 600kv. from accelerator 24. The beam current of 300 microamperes wasnecessary to replace the leakage currents I load current I and providesufiicient electrons to the wall of chamber 14 to maintain theself-regulating operation.

It is to be noted that the examples given for the embodiments of FIG. 1and FIG. 2 are merely illustrative of voltages obtainable using thepresent invention and that the present invention is not to be limited tothe values of the elements in each of the embodiments. It is to befurther noted that for the practice of the present invention, neitherelectrode 10 nor chamber 14 has to be grounded but that they may be atsome other electrical potential.

Persons skilled in the art will, of course, readily adapt the teachingsof the invention to methods and embodiments far dilferent than themethods and embodiments herein described. Accordingly, the scope of theprotection afforded the invention should not be limited to theparticular embodiments and methods described and shown above but shouldbe determined only in accordance with the appended claims.

What is claimed is:

1. A device for producing a high voltage between first and secondelectrodes mounted in a partial vacuum, comprising means for generatingan electron beam, a Faraday cup mounted in electrical contact with saidfirst electrode, means for directing said electron beam into said cup tocause a negative charge accumulation on said first electrode, whereby ahigh voltage is developed between said first and second electrodes.

2. The device according to claim 1, further including a resistorconnected between said first electrode and electrical ground.

3. The device according to claim 2 wherein said resistor has aresistance value substantially lower than the resistance existingbetween said first electrode and electrical ground and the resistancebetween said first and second electrodes.

4. The device according to claim 1 wherein said Faraday cup has aminimum diameter of approximately two inches.

5. The device according to claim 1 wherein said Faraday1 cup has aminimum length to diameter ratio of 6 to 6. A device for producing ahigh voltage between first and second electrodes mounted approximately10 cm. apart in a partial vacuum, comprising means for generating anelectron beam having an energy of 800 kv. and a current of microamperes,a Faraday cup mounted in electrical contact with said first electrode, a5 l0 -ohm resistor connected between said first electrode and electricalground, means for electrically grounding said second electrode,means'for directing said electron beam into said Faraday cup to cause anegative charge accumulation on said first element, whereby a voltage ofapproximately 600 kv. is developed between said first and secondelectrodes.

7. A device for producing a high voltage between first and secondelectrodes mounted in a partial vacuum, comprising means for generatingan electron beam having an energy of 600 kv. and a current of 300microamperes, a Faraday cup 18 inches long x 3 inches wide x 2.5 incheshigh mounted in electrical contact with said first electrode, means forelectrically grounding said second electrode and means for directingsaid electron beam into said cup to cause a negative charge accumulationon said first electrode, whereby a voltage of 600 kv. is developedbetween said first and second electrodes.

References Cited UNITED STATES PATENTS Coolidge 3105 XR Labin et al.315-3 Snyder 315 XR Gale et al. 3105 XR 6 Gale 3106 XR Gale 315-3 Goldie31363 Gale 310-6 XR Rose 25049.5 Goncz 313106 MILTON O. HIRSHFIELD,Primary Examiner. D. F. DUGGAN, Assistant Examiner.

7. A DEVICE FOR PRODUCING A HIGH VOLTAGE BETWEEN FIRST AND A SECONDELECTRODES MOUNTED IN A PARTIAL VACUUM, COMPRISING MEANS FOR GENERATINGAN ELECTRON BEAM HAVING AN ENERGY OF 600 KV. AND A CURRENT OF 300MICROAMPERES, A FARADAY CUP 18 INCHES LONG X 3 INCHES WIDE X 2.5 INCHESHIGH MOUNTED IN ELECTRICAL CONTACT WITH SAID FIRST ELECTRODE, MEANS FORELECTRICALLY GROUNDING SAID SECOND ELECTRODE AND MEANS FOR DIRECTINGSAID ELECTRON BEAM INTO SAID CUP TO CAUSE A NEGATIVE CHARGE ACCUMULATIONON SAID FIRST ELECTRODE, WHEREBY A VOLTAGE OF 600 KV. IS DEVELOPEDBETWEEN SAID FIRST AND SECOND ELECTRODES.